This revised competing renewal application for 2R01DA011946 (requesting funding for years 12-16) is in response to PA-10-268 that promotes research to understand the neurobiological mechanisms underlying all phases of drug addiction, including....relapse, as well as the effects of pharmacological treatments aimed at curbing substance use. An understanding of the neurobiological mechanisms underlying drug addiction can help to identify targets for prevention and treatment interventions. Tobacco smoking, attributed partly to the addictive properties of nicotine, is a chronic relapsing disorder The majority of smokers who attempt to quit relapse within one month. Conditioned motivational effects of smoking-related cues contribute to this chronic vulnerability to relapse amongst abstinent smokers. Thus, blockade of the motivational impact of smoking- related cues or enhancement of extinction learning and memory using pharmacological treatments are possible strategies to prolong abstinence in smokers. Glutamate plays a critical role in the development of nicotine dependence. Importantly, studies suggest that enhancing glutamatergic transmission during extinction training can facilitate extinction of fear and conditioned drug-associated memories, while exposure to drug- associated cues enhances glutamatergic transmission resulting in reinstatement of drug seeking. Based on these findings, the overall hypothesis of this project is that enhancing glutamate transmission during extinction will facilitate extinction learning and decrease subsequent cue-induced nicotine seeking. In contrast, blockade of increased glutamate transmission in response to nicotine-associated cues will attenuate reinstatement of nicotine seeking. Specific Aim 1 will assess the effects of blockade of glutamatergic transmission, by targeting either the AMPA or metabotropic glutamate 2 (mGlu2) or metabotropic glutamate 5 (mGlu5) receptors, on cue- induced reinstatement of nicotine seeking. Specific Aim 2 will assess the effects of pharmacological treatments that subtly increase glutamate transmission via either AMPA, mGlu5 or mGlu2/3 receptors on extinction of nicotine seeking and subsequent cue-induced reinstatement of nicotine seeking. Different brain regions and circuits mediate extinction and cue-induced reinstatement of drug seeking. Thus, it is hypothesized that the nucleus accumbens (NAcc) shell plays an important role in extinction learning, while the NAcc core is more involved in drug seeking. Hence, Specific Aim 3 will assess the effects of viral-vector mediated increased expression of AMPA receptor subunits (GluR1 and GluR2) in the NAcc core and shell on extinction training and subsequent cue-induced reinstatement of nicotine seeking. Using a combination of state-of-the-art behavioral, pharmacological, anatomical and molecular techniques, the proposed studies will promote our understanding of the neuromechanisms and neuroanatomical sites mediating extinction of nicotine seeking, and cue-induced reinstatement of nicotine seeking. The findings will identify pharmacological approaches for the prevention of relapse, and thus promote abstinence from the harmful tobacco smoking habit.